1. Field of the Invention
The present invention relates to a thermally-assisted type magnetic head.
2. Description of the Related Art
In recent years, in association with the high recording density of magnetic recording devices such as hard disk devices, there has been a demand for improvement in the performance of thin film magnetic heads and magnetic recording media. Composite-type thin film magnetic heads have been widely used for the thin film magnetic head. The composite-type thin film magnetic head includes a reproducing head having a magneto resistive effect element (hereafter, referred to as an MR element) for reading and a recording head having an inductive electromagnetic transducer (a magnetic recording element) for writing, with both heads being laminated on a substrate. The thin film magnetic head incorporated in the hard disk device flies just above a surface of the magnetic recording medium during recording and reproducing processes.
The magnetic recording medium is a discontinuous medium where magnetic microparticles gather. Each of the microparticles has a single magnetic domain structure. In the magnetic recording medium, one recording bit is structured with a plurality of magnetic microparticles. In order to increase the recording density, asperity of a boundary between adjacent recording bits needs to be small. For this, the size of the magnetic microparticles needs to be decreased. However, when the size of the magnetic microparticles is decreased, the volume of the microparticles decreases. Accordingly, thermal stability of magnetization of the magnetic microparticles also decreases. In order to solve this problem, increasing anisotropic energy of the magnetic microparticles is effective. However, when the anisotropic energy of the magnetic microparticles is increased, the coercive force of the magnetic recording medium is also increased. As a result, it becomes difficult to record information with a conventional magnetic head. Conventional magnetic recording has such a drawback, and this is a large obstacle to achieving an increase in the recording density.
To solve this problem, one method known as so-called thermally-assisted magnetic recording is proposed. This method uses a magnetic recording medium having a large coercive force. A magnetic field and heat are simultaneously added to a part of the magnetic recording medium where information is recorded when information is recorded. With this method, the temperature of the part where the information is recorded is increased. Therefore, the coercive force decreases, and the information is able to be recorded.
In thermally-assisted magnetic recording, a method that uses near field light is known as a method to provide heat to the magnetic recording medium. The near field light is a type of electromagnetic field that is generated around a substance. Ordinary light cannot be focused to a region that is smaller than its wavelength due to diffraction limitations. However, when light having an identical wavelength is irradiated on to a microstructure, near field light corresponding to the scale of the microstructure is generated, enabling the light to be focused on to a minimal region, such as a region only tens of nm in size. As a practical method to generate the near field light, a method to generate laser light using a laser diode and to generate the near field light from plasmon excited by the laser light is generally known. The near field light is generated with a metal that is referred to as a probe that is a plasmon antenna.
Direct irradiation of light generates the near field light in the plasmon antenna. However, with this method, a conversion efficiency to convert irradiated light into the near field light is low. Most of the energy of the light irradiated to the plasmon antenna reflects from the surface of the plasmon antenna or is converted into thermal energy. The size of the plasmon antenna is set to be the wavelength of the light or less. Accordingly, the volume of the plasmon antenna is small. Therefore, the temperature of the plasmon antenna significantly increases as a result of the above-described generation of heat.
Due to the temperature increase, the volume of the plasmon antenna expands, and the plasmon antenna protrudes from an air bearing surface that is a surface facing the magnetic recording medium. Accordingly, the distance of an edge part of the MR element positioned on the air bearing surface from the magnetic recording medium increases. As a result, a problem in which servo signals recorded on the magnetic recording medium are barely sensed during the recording process.
Currently, a technology that does not directly irradiate light to the plasmon antenna is proposed. For example, there is a known technology where propagating light entering from a laser diode and propagating through a core of a waveguide such as an optical fiber is coupled in a surface plasmon polariton mode through a buffer portion to a plasmon generator so that the surface plasmon is excited in the plasmon generator. The plasmon generator includes an edge of plasmon generator that is positioned on the air bearing surface and that generates the near field light, and a propagation edge facing the waveguide through the buffer portion. At the interface between the core and the buffer portion, the light propagating through the core is totally reflected. However, at the same time, light penetrating to the buffer portion is generated, which is referred to as evanescent light. When the evanescent light and collective oscillation of charges in the plasmon generator are coupled, the surface plasmon is excited in the plasmon generator. The excited surface plasmon propagates to the edge of plasmon generator along the propagation edge, and generates the near field light at the edge of plasmon generator. According to this technology, the light propagating through the core is not directly irradiated to the plasmon generator so that an excessive temperature increase in the plasmon generator can be prevented.
The laser light emitted from the laser diode preferably propagates to the vicinity of the air bearing surface through a straight-shaped path in order to prevent generation of propagation loss. Variation of a propagating direction of propagating light due to reflection, refraction or the like contributes to generate large propagation loss. For this, the laser diode is preferably attached such that an outgoing surface of the laser diode faces the air bearing surface of the magnetic head slider, i.e., such that an outgoing direction of laser light is orthogonal to the air bearing surface. If the laser diode is attached as described above, the propagating light propagates straight to the vicinity of the air bearing surface without the propagating direction being changed along the way.
In order to attach the laser diode such that the outgoing surface of the laser diode faces the air bearing surface of the magnetic head slider, the laser diode needs to be attached on a backside surface of the air bearing surface of the magnetic head slider. Such an example is disclosed in Japanese laid-open patent application publication number 2008-47268.
The magnetic head slider is manufactured by making a large number of magnetic head sliders on a wafer and cutting the wafer into individual magnetic head sliders. The backside surface is hidden inside the wafer in a wafer state, and the backside surface is first exposed when the wafer is cut into row bars. Therefore, a step for attaching the laser diode to the magnetic head slider is performed at the earliest after the wafer is cut into the row bars. Ordinarily, the laser diode is attached to each slider after a step of separating into the sliders. As described above, it is impossible in principle to attach the laser diode on the backside surface of the air bearing surface of the magnetic head slider during the wafer process. This is a serious problem from a standpoint of manufacturing efficiency of the magnetic head.
To maximize the manufacturing efficiency of the magnetic head, it is desirable to attach the laser diode to the wafer during the wafer process. In this case, an attached surface of the laser diode necessarily is an opposite-side surface of a substrate of the wafer (a lamination direction upper surface in the wafer process). In such a configuration, laser light emitted from the laser diode needs to be turned 90 degrees at least once on the path. As a method to achieve this, a method using mirrors is known.
In Japanese laid-open patent application publication number 2007-142227, a bent waveguide where a plurality of corner mirrors is disposed is disclosed. Each corner mirror is formed by obliquely chamfering a corner of a semiconductor at 45 degrees by etching. The light reflects due to the difference of refractive indices of the semiconductor and air on a chamfered surface, and propagates through the waveguide.
In Japanese laid-open patent application publication number 2008-59645, a thermally-assisted type magnetic head providing a mirror configuration is disclosed. A laser diode is disposed on the outside of the magnetic head slider, and an edge surface of an active layer sandwiched by cladding layers is obliquely formed. The laser light is emitted from the laser diode, immediately turns 90 degrees, and then enters the waveguide in the slider.
However, with the method using the mirrors as described above, a large loss in the propagating efficiency occurs when the propagating light is reflected.
The object of the present invention is to provide a magnetic head of a thermally-assisted magnetic recording system where laser light emitted from the laser diode reflects to be introduced into the core, and to a magnetic head of the thermally-assisted magnetic recording system which improves manufacturing efficiency and has a small propagation loss associated with the propagating light.